E g y p t FORTY-ONE FIGURESCertain important problems relating to the biology of schistosomes in the definitive host have not been solved, and are still a matter of discussion. Among these problems is the classification of the growth stages of the young worms from penetration to the attainment of the adult condition. A c1,assification of growth stages is of great importance in soiving many problems connected with the life of the parasite in the definitive host, such as the route taken by these worms from the time they invade the skin until they reach their final location in the veins of the portal system, the effect of infection on the worms introduced later, and the influence of one sex on the development of the other. I n the past, criteria used for classifying growth stages of post-cercarial forms of schistosomes have been the attainment of certain sizes of body and suckers and of certain stages of development of the digestive and excretory system. Katsurada ('13) compared the sizes of adult males and females of Schistosoma japonicum reported by several in-Contribution from the Department of Zoology, University of Michigan. I wish to thank Dr. George R. LaRue for his interest and very helpful criticism during the progress of this work. Due credit is given to the Laboratory of Vertebrate Biology, University of Michigan, for supplying large numbers of Perom yscus manimlatus used in the experiments.

Spinosyns are new neurotoxins mixtures produced during fermentation of a soil actinomycete that have high activity towards different pests. Spinosyns compounds were represented in Spinosad and its evoluted compound ,Spinetoram ,which were tested for their toxic effects under laboratory conditions against adult females of Aphis gossypii Glover and Tetranychus urticae Koch ,and the fourth instar larvae of Spodoptera littoralis (Boisd.)by leaf-dip technique. Spinosad LC50's of A. gossypii , T. urticae and S. littoralis were 30.417,25.982 and 5.379 ppm, respectively but they were 0.596,0.370 and 1.742 ppm,respectively in case of Spinetoram.The superior Spinosyn compounds,Spinetoram gained the best results against piercing-sucking pests compared with Spinosad which was the best against S. littoralis ,so the present histological studies were concerned with Spinetoram.Each pest was treated with its LC50 value. Histological defects after treatments in the neuromuscular nicotinic receptors were detected and discussed.

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